The present disclosure relates to methods for forming films on substrates.
There is a continuing need for efficient methods for producing films on substrates; particularly thin films made from polymeric materials. Formation of films from particles deposited on substrate surfaces can be accomplished by a variety of methods such as thermal sintering and chemical crosslinking or curing. In all of these methods, the glass transition temperature (Tg) of the particles is an important factor during film formation. In prior art methods film formation typically occurs only at temperatures higher than the Tg of the particles. The Tg of some commercially available materials can be in the range of about 20xc2x0 C. (e.g., poly(butyl methacrylate)) to an excess of about 200xc2x0 C. (e.g., poly(bisphenol A terephthalate)). At such high temperatures, the amount of heat required for film formation can lead to the chemical decomposition of the particles, complicate control of the film formation process for achieving desirable film properties, consume energy, and damage or otherwise negatively alter a temperature-sensitive substrate.
Disclosed herein are methods for forming a continuous film on a substrate surface that involve depositing particles onto a substrate surface and contacting the particle-deposited substrate surface with a supercritical fluid under conditions sufficient for forming a continuous film from the deposited particles. A further method for forming a film on a substrate surface involves depositing particles having a mean particle size of less than 1 micron onto a substrate surface and contacting the particle-deposited substrate surface with a supercritical fluid under conditions sufficient for forming a film from the deposited particles.
The methods can be performed by providing a pressure vessel that can contain a compressible fluid. A particle-deposited substrate is provided in the pressure vessel and the compressible fluid is maintained at a supercritical or sub-critical state sufficient for forming a film from the deposited particles.